The incidence of traumatic brain injury (TBI) rises during adolescence, a period of marked changes in brain maturation, cognition, behavior, and social function. Moderate to severe TBI (MSTBI) in adolescents disrupts executive functions, i.e., superordinate, managerial cognitive abilities such as reasoning, strategy application, perspective-taking, and behavioral regulation, which we postulate mediate impairment of social cognition that leads to persistent psychosocial maladjustment. However, there is a paucity of research concerning the executive cognitive and social cognitive sequelae of MSTBI and their associated neural mechanisms in this high risk population. Lack of naturalistic executive function and social cognitive tasks designed from a cognitive neuroscience perspective, and insensitive brain imaging methods have constrained advances in clinical assessment and rehabilitation of adolescents after MSTBI. To close this gap in knowledge, we request four years of support to prospectively study 94 MSTBI patients age 12 to 18 years old and for comparison, 94 orthopedic injury (OI) patients of similar age whom we screen at about one month post-injury for pre-injury neuropsychiatric conditions and follow-up at 12 months post-injury with multimodality brain imaging and behavioral assessments. Aim 1 evaluates executive functions, behavioral regulation, and social cognition using naturalistic, virtual tasks, performance measures, and self-report, and addresses the mediation of social cognitive deficit following MSTBI by executive function and behavioral regulation. Aim 2 examines neural mechanisms of impaired executive function and social cognition post-MSTBI by integrating data on brain region volumes from magnetic resonance imaging (MRI), integrity of white matter connecting prefrontal, posterior, and subcortical brain regions using diffusion tensor imaging (DTI), and brain activation associated with making social attributions during functional MRI (fMRI). Aim 2 also integrates data from the imaging modalities with behavioral findings from Aim 1. Aim 3 addresses the contribution of executive function and social cognitive deficits to psychosocial maladjustment, measured by behavioral rating scales and interviews with patients, parents, and teachers. In Aim 3 we also propose to evaluate the contribution of executive function data acquired from naturalistic, performance-based tasks to psychosocial adjustment. The moderating role of the family environment in the impact of MSTBI on psychosocial adjustment is also investigated in Aim 3. Control procedures to take account of the effects of language, emotional distress, and other potential confounds on executive function, social cognition, and brain imaging variables are proposed. General linear model and generalized linear model procedures are proposed to address the Aims. Dissemination of the executive function, social cognition, brain imaging, and psychosocial outcome data to address the Aims will impact public health through guiding advances in clinical assessment and rehabilitation of adolescents who sustain MSTBI.